Coping With Water Shortage: An Update on the Role of K+, Cl-, and Water Membrane Transport Mechanisms on Drought Resistance

Drought is now recognized as the abiotic stress that causes most problems in agriculture, mainly due to the strong water demand from intensive culture and the effects of climate change, especially in arid/semi-arid areas. When plants suffer from water deficit (WD), a plethora of negative physiological alterations such as cell turgor loss, reduction of CO2 net assimilation rate, oxidative stress damage, and nutritional imbalances, among others, can lead to a decrease in the yield production and loss of commercial quality. Nutritional imbalances in plants grown under drought stress occur by decreasing water uptake and leaf transpiration, combined by alteration of nutrient uptake and long-distance transport processes. Plants try to counteract these effects by activating drought resistance mechanisms. Correct accumulation of salts and water constitutes an important portion of these mechanisms, in particular of those related to the cell osmotic adjustment and function of stomata. In recent years, molecular insights into the regulation of K+, Cl-, and water transport under drought have been gained. Therefore, this article brings an update on this topic. Moreover, agronomical practices that ameliorate drought symptoms of crops by improving nutrient homeostasis will also be presented

Disconnected contributions to D-meson semi-leptonic decay form factors

We calculate the disconnected contribution to the form factor for the semileptonic decay of a D-meson into a final state, containing a flavor singlet eta meson. We use QCDSF n_f=2+1 configurations at the flavor symmetric point m_u=m_d=m_s and the partially quenched approximation for the relativistic charm quark. Several acceleration and noise reduction techniques for the stochastic estimation of the disconnected loop are tested.Comment: 7 pages, talk presented at the XXIX International Symposium on Lattice Field Theory (Lattice 2011), July 10-16, 2011, Squaw Valley, Lake Tahoe, California, US

Chemical factors controlling the steady-state distribution of mixed carbonate-siliciclastic sediments in Bayona Bay (northwest Spain)

The relative space distributions of single mineral constituents in mixed terrigenous-carbonated sediments of the Bayona Bay have been analysed. In order to determine the existence of different mixing mechanisms, a study comparing the general sedimentary trends resulting from the average patterns and the single mineral behaviour, reflected in the single-mineral mapping, was carried out. The relative abundance of all mineral phases in surface sediment samples was first determined by quantitative X-ray powder diffraction data, using the Rietveld method. This procedure enabled us to create specific maps for both the minerals forming the terrigenous fraction and the different calcium carbonate polymorphs involved in the carbonatic component. A cross-linked behaviour between the carbonate facies and the terrigenous minerals involved in the calcium carbonate generation was found, suggesting the existence of a chemical control mechanism which, through dissolution-crystallization processes, constrains the mixed environment's long-term evolution. In the general framework of the region studied, these relations operate for the relative amount of plagioclase to calcium carbonate. The existence of dissolution and growth between both minerals, favoured by the high rate of removal, is proposed, yielding a final crossed pattern, representative of the steady-state. Furthermore, a specific analysis, restricted to the region of low rate of material removal and maximum amount of intermixed sediments, clearly shows an anisotropic distribution for every calcium carbonate polymorph (calcite and aragonite). These correlate with the biotite distribution, and can be connected to local variations in seawater Mg/Ca ratio, induced by biotite weathering.En este trabajo se analiza de forma específica la distribución espacial de cada uno de los minerales involucrados en sedimentos mixtos terrígenos-carbonatados de la bahía de Bayona y se compara con la distribución global de sedimentos, tal como resulta de análisis granulométricos, con el fin de determinar la existencia de diferentes mecanismos de mezcla entre los minerales de ambas fracciones. El contenido porcentual en peso de cada fase mineral, en muestras superficiales de sedimento, se determinó a partir de datos cuantitativos de DRX, empleando el método de Rietveld. Este procedimiento nos ha permitido realizar mapas específicos de distribución, tanto para cada mineral de la fracción terrígena como para cada uno de los diferentes polimorfos de carbonato cálcico en la componente carbonatada. Como resultado de este estudio comparativo, se ha encontrado una correlación, en la distribución espacial y granulométrica, de las facies carbonatadas y los minerales terrígenos implicados en la generación de carbonato cálcico. Un posterior análisis de este resultado sugiere la presencia de mecanismos químicos de control que regulan la interacción entre siliciclastos y carbonatos mediante procesos de disolución-cristalización mediados por el agua del mar. El estudio se ha realizado a dos escalas. En el ámbito general de la bahía de Bayona, las relaciones de distribución observadas entre plagioclasas y carbonato cálcico pueden ser explicadas, dentro del balance global del Ca³⁺ disuelto en el agua del mar, mediante la meteorización química de las plagioclasas y la consiguiente generación de carbonatos. En este caso, los patrones de distribución reflejan la aproximación a un estado estacionario mediante sucesivos eventos de mezcla asociados a la alta removilización material en el medio, tanto para la distribución porcentual en peso como para la distribución granulométrica entre ambos minerales. Finalmente, se realiza un análisis particularizado en una región con baja tasa de removilización y donde la interacción entre sedimentos de ambas fracciones es máxima. El resultado muestra claramente una distribución espacial anisótropa para cada uno de las fases de carbonato cálcico (calcita y aragonito). La abundancia relativa de cada uno de los polimorfos, así como el contenido en Mg³⁺ de la calcita, ha sido correlacionado con la distribución de la biotita y explicado a partir de las diferencias de solubilidad en función de la alta relación Mg³⁺ /Ca³⁺ en el agua de mar que resulta, localmente, de la meteorización química de dicho mineral.Instituto Español de Oceanografí

The effects of stand characteristics on the understory vegetation in Quercus petraea and Q. cerris dominated forests

The shelterwood system used in Hungary has many effects on the composition and structure of the herb layer. The aim of our study was to identify the main variables that affect the occurence of herbs and seedlings in Turkey oak-sessile oak (Quercus cerris and Q. petraea) stands. The study was carried out in the Bükk mountains, Hungary. 122 sampling plots were established in 50-150 year old oak forests, where we studied the species composition and structure of the understorey and overstorey. The occurence of herbs was affected by canopy closure, the heterogenity and patchiness of the stand, the slope and the east-west component of the aspect. The composition of saplings was significantly explained by the ratio of the two major oak species in the stand and the proximity of the adult plants. An important result for forest management was that sessile oaks were able to regenerate almost only where they were dominant in the overstorey

Priority sites for wildfowl conservation in Mexico

A set of priority sites for wildfowl conservation in Mexico was determined using contemporary count data (1991–2000) from the U.S. Fish & Wildlife Service mid-winter surveys. We used a complementarity approach implemented through linear integer programming that addresses particular conservation concerns for every species included in the analysis and large fluctuations in numbers through time. A set of 31 priority sites was identified, which held more than 69% of the mid-winter count total in Mexico during all surveyed years. Six sites were in the northern highlands, 12 in the central highlands, six on the Gulf of Mexico coast and seven on the upper Pacific coast. Twenty-two sites from the priority set have previously been identified as qualifying for designation as wetlands of international importance under the Ramsar Convention and 20 sites are classified as Important Areas for Bird Conservation in Mexico. The information presented here provides an accountable, spatially-explicit, numerical basis for ongoing conservation planning efforts in Mexico, which can be used to improve existing wildfowl conservation networks in the country and can also be useful for conservation planning exercises elsewhere

A first-principles approach to electrical transport in atomic-scale nanostructures

We present a first-principles numerical implementation of Landauer formalism for electrical transport in nanostructures characterized down to the atomic level. The novelty and interest of our method lies essentially on two facts. First of all, it makes use of the versatile Gaussian98 code, which is widely used within the quantum chemistry community. Secondly, it incorporates the semi-infinite electrodes in a very generic and efficient way by means of Bethe lattices. We name this method the Gaussian Embedded Cluster Method (GECM). In order to make contact with other proposed implementations, we illustrate our technique by calculating the conductance in some well-studied systems such as metallic (Al and Au) nanocontacts and C-atom chains connected to metallic (Al and Au) electrodes. In the case of Al nanocontacts the conductance turns out to be quite dependent on the detailed atomic arrangement. On the contrary, the conductance in Au nanocontacts presents quite universal features. In the case of C chains, where the self-consistency guarantees the local charge transfer and the correct alignment of the molecular and electrode levels, we find that the conductance oscillates with the number of atoms in the chain regardless of the type of electrode. However, for short chains and Al electrodes the even-odd periodicity is reversed at equilibrium bond distances.Comment: 14 pages, two-column format, submitted to PR